Can an anaphylactic reaction occur days after the allergens? for example a bee sting ?

Not likely: Anaphlactic reaction is not likely to occur days after a bee sing unless you are bitten again.

No: Anaphylaxis means a severe or life threatening allergic reaction. Regardless, an allergic reaction to a bee sting would happen within seconds. Minutes tops. There may be mild or no reaction to the first sting, but you can become sensitized so that a second sting can cause a severe reaction. If you swallow an allergen the reaction may be delayed several hours max for a type 1 hypersensitivity rxn.